Diaporthe helianthi

Diaporthe helianthi is a fungal pathogen that causes Phomopsis stem canker of sunflowers. In sunflowers, Phomopsis helianthi (teleomorph =Diaporthe helianthi) is the causative agent behind stem canker. Its primary symptom is the production of large canker lesions on the stems of sunflower plants. These lesions can eventually lead to lodging and plant death. This disease has been shown to be particularly devastating in southern and eastern regions of Europe, although it can also be found in the United States and Australia. While cultural control practices are the primary method of controlling for Stem Canker, there have been a few resistant cultivars developed in regions of Europe where the disease is most severe.

from Wikipedia